Golf ball

ABSTRACT

The present invention is a golf ball having a core and a cover. The core has a diameter of 1.53 inches to 1.55 inches, and a PGA compression of 60 to 75 points. The cover has a thickness of 0.60 inch to 0.90 inch. The cover has a Shore D hardness less than 58 as measured on the land surface of the golf ball. The golf ball has a has a COR that is greater than 0.782 points at 143 feet per second.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part application of co-pending U.S. patent application No. 09/768,846, filed on Jan. 23, 2001, and hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to a golf ball. More specifically, the present invention relates to a two-piece golf ball with a cover layer composed of an ionomer blend and a core containing polybutadiene, tungsten, and other materials.

[0005] 2. Description of the Related Art

[0006] Two-piece golf balls with ionomer covers have been in existence since the 1960's. The core is typically solid, and the cover is usually a hard ionomer material. The two-piece golf balls of the prior art provide added distance while giving up feel.

BRIEF SUMMARY OF THE INVENTION

[0007] One aspect of the present invention is a golf ball having a core and a cover. The core has a diameter of 1.53 inches to 1.55 inches. The core is composed of polybutadiene, zinc oxide in an amount of 7 to 15 parts per hundred parts of polybutadiene, zinc diacryalate in an amount of 30 to 50 parts per hundred parts of polybutadiene, an initiator in an amount of 0.1 to 1.0 parts per hundred parts of polybutadiene, and tungsten in an amount of 5 to 10 parts per hundred parts of polybutadiene. The core has a PGA compression of 60 to 75 points. The cover has a thickness of 0.60 inch to 0.90 inch. The cover is composed of an ionomer blend formed from a high acid ionomer resin neutralized with sodium and a terpolymer neutralized with magnesium. The cover has a Shore D hardness ranging from 52 to 58. The golf ball has a COR at 143 feet per second that is greater than 0.782 points.

[0008] Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0009]FIG. 1 is an equatorial view of a preferred embodiment of a golf ball of the present invention.

[0010]FIG. 2 is a cross-sectional view of a golf ball of the present invention.

[0011]FIG. 3 is a graph of the Coefficient of Restitution (COR) for a golf ball (y-axis) and the Shore D of the cover (x-axis) for the golf ball of the present invention and 12 competitor golf balls.

[0012]FIG. 4 is a graph of the Coefficient of Restitution (COR) for a golf ball (y-axis) and the ball compression (x-axis) for the golf ball of the present invention and 12 competitor golf balls.

[0013]FIG. 5 is a graph of the Coefficient of Restitution (COR) for a golf ball (y-axis) and the core size (x-axis) for the golf ball of the present invention and 12 competitor golf balls.

DETAILED DESCRIPTION OF THE INVENTION

[0014] As shown in FIGS. 1 and 2, the golf ball of the present invention is generally designated 10. The golf ball 10 has a core 12 and a cover 14 encompassing the core. The surface of the cover 14 has an aerodynamic pattern thereon composed of a plurality of dimples. A preferred aerodynamic pattern is disclosed in co-pending U.S. patent application No. 09/768,847 filed on Jan. 23, 2001, entitled Aerodynamic Pattern For A Two-Piece Golf Ball, which pertinent parts are hereby incorporated by reference.

[0015] The golf ball 10 of the present invention is directed at a two-piece golf ball that has a relatively soft cover 14 encompassing a core 12 with a relatively soft core compression. The construction of the golf ball 10 allows for a golf ball 10 that has a softer cover while providing greater velocity and better spin than other competitive golf balls.

[0016] The core 12 of the golf ball 10 is the “engine” for the golf ball 10 such that the inherent properties of the core 12 will strongly determine the initial velocity and distance of the golf ball 10. A higher initial velocity will usually result in a greater overall distance for a golf ball. In this regard, the Rules of Golf, approved by the United States Golf Association (“USGA”) and The Royal and Ancient Golf Club of Saint Andrews, limits the initial velocity of a golf ball to 250 feet (76.2 m) per second (a two percent maximum tolerance allows for an initial velocity of 255 per second) and the overall distance to 280 yards (256 m) plus a six percent tolerance for a total distance of 296.8 yards (the six percent tolerance may be lowered to four percent). A complete description of the Rules of Golf are available on the USGA web page at www.usga.org. Thus, the initial velocity and overall distance of a golf ball must not exceed these limits in order to conform to the Rules of Golf. Therefore, the core 12 for a USGA approved golf ball is constructed to enable the golf ball 10 to meet, yet not exceed, these limits.

[0017] The coefficient of restitution (“COR”) is a measure of the resilience of a golf ball. The COR is a measure of the ratio of the relative velocity of the golf ball after direct impact with a hard surface to the relative velocity before impact with the hard surface. The COR may vary from 0 to 1, with 1 equivalent to a completely elastic collision and 0 equivalent to a completely inelastic collision. A golf ball having a COR value closer to 1 will generally correspond to a golf ball having a higher initial velocity and a greater overall distance. The force of a club during a swing is transferred to a golf ball. If the golf ball has a high COR (more elastic), then the initial velocity of the golf ball will be greater than if the golf ball had a low COR. In general, a higher compression core will result in a higher COR value. The COR of the core 12 of the golf ball 10 of the present invention is preferably 75 to 80 points at 143 feet per second (“fps”), most preferably ranging from 78.0 to 79.5 points at 143 fps,”), even more preferably ranging from 78.5 to 79.4 points at 143 fps, and is most preferably 79.0 points at 143 fps.

[0018] In the present invention, the core components are mixed and compression molded in a conventional manner known to those skilled in the art. In a preferred form, the finished core 12 has a diameter of about 1.50 inch to about 1.62 inch for a golf ball 10 having an outer diameter of 1.68 inches, and is most preferably 1.535 to 1.545, with 1.54 the preferable diameter of the core 12. The core weight is preferably maintained in the range of about 32 to about 40 g, with 34 grams to 38 grams a more preferably range and 37 grams the most preferable weight of the core 12. The core PGA compression is preferably maintained in the range of about 60 to 80, and most preferably range about 65 to 75 with 70 the most preferable core compression.

[0019] As used herein, the term “PGA compression” is defined as follows:

PGA compression value=180−Riehle compression value

[0020] The Riehle compression value is the amount of deformation of a golf ball in inches under a static load of 200 pounds, multiplied by 1000. Accordingly, for a deformation of 0.095 inches under a load of 200 pounds, the Riehle compression value is 95 and the PGA compression value is 85.

[0021] The core 12 of the golf ball 10 is generally composed of a blend of a base rubber, a cross-linking agent, a free radical initiator, tungsten and one or more fillers or processing aids. A preferred base rubber is a polybutadiene having a cis-1,4 content above 90%, and more preferably 98% or above.

[0022] The use of cross-linking agents in a golf ball core is well known, and metal acrylate salts are examples of such cross-linking agents. For example, metal salt diacrylates, dimethacrylates, or mono(meth)acrylates are preferred for use in the golf ball cores of the present invention, and zinc diacrylate is a particularly preferred cross-linking agent. A commercially available suitable zinc diacrylate is SR-416 available from Sartomer Co., Inc., Exton, Pa. Other metal salt di- or mono-(meth)acrylates suitable for use in the present invention include those in which the metal is calcium or magnesium. In the manufacturing process it may be beneficial to pre-mix some cross-linking agent(s), such as, e.g., zinc diacrylate, with the polybutadiene in a master batch prior to blending with other core components. A preferred mixing process is disclosed in co-pending U.S. patent application No. 09/690,373 filed on Oct. 16, 2000, entitled A Process For Manufacturing A Core For A Golf Ball, which pertinent parts are hereby incorporated by reference.

[0023] Free radical initiators are used to promote cross-linking of the base rubber and the cross-linking agent. Suitable free radical initiators for use in the golf ball core 12 of the present invention include peroxides such as dicumyl peroxide, bis-(t-butyl peroxy) diisopropyl benzene, t-butyl perbenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-5-butylperoxy-hexane, 1,1-di (t-butylperoxy) 3,3,5-trimethyl cyclohexane, and the like, all of which are readily commercially available.

[0024] Zinc oxide is also preferably included in the core formulation. Zinc oxide may primarily be used as a weight adjusting filler, and is also believed to participate in the cross-linking of the other components of the core (e.g. as a coagent). Additional processing aids such as dispersants and activators may optionally be included. In particular, zinc stearate may be added as a processing aid (e.g. as an activator).

[0025] Tungsten is added to the core mixture to provide weight to the core 12, and hence the golf ball 10, while occupying volume minimal volume. Tungsten has a density of 19.3 grams per centimeter cubed which is much greater than the density of the polybutadiene. Thus, minimal tungsten allows for the necessary weight while allowing for more polybutadiene to be used in the core 12 to provide greater velocity. A number of other specific gravity adjusting fillers, in addition to the tungsten, may be included to obtain a preferred total weight of the core 12. Examples of such fillers include clay and barium sulfate. All such processing aids and fillers are readily commercially available. The present inventors have found a particularly useful tungsten filler is WP102 Tungsten (having a 3 micron particle size) available from Atlantic Equipment Engineers (a division of Micron Metals, Inc.), Bergenfield, N.J.

[0026] Table 1 below provides the ranges of materials included in the preferred core formulations of the present invention. TABLE ONE Core Formulations Component Preferred Range Most Preferred Range Polybutadiene 100 parts 100 parts Zinc diacrylate 20-35 ph 25-30 phr Zinc oxide 0-50 ph 5-15 phr Zinc stearate 0-15 ph 1-7 phr Peroxide 0.2-2.5 phr 0.5-1.5 phr Filler As desired As desired Tungsten 6-10 phr 6 phr

[0027] The preferred specific gravity for the core 12 is 1.165 to 1.185, and most preferably 1.174.

[0028] The cover 14 preferably is composed of a thermoplastic material (e.g. thermoplastic or thermoplastic elastomer) or a blend of thermoplastic material (e.g. metal containing, non-metal containing or both). Most preferably the cover 14 is composed of a blend of thermoplastic materials that contain organic chain molecules and metal ions. The metal ion may be, for example, sodium, zinc, magnesium, lithium, potassium, cesium, or any polar metal ion that serves as a reversible cross-linking site and results in high levels of resilience and impact resistance. Suitable commercially available thermoplastics are ionomers based on ethylene copolymers and containing carboxylic acid groups with metal ions such as described above. The acid levels in such suitable ionomers may be neutralized to control resiliency, impact resistance and other like properties.

[0029] In addition, other fillers with ionomer carriers may be used to modify (e.g. preferably increase) the specific gravity of the thermoplastic blend to control the moment of inertia and other like properties. Exemplary commercially available thermoplastic materials suitable for use in a cover 14 of a golf ball 10 of the present invention include, for example, the following materials and/or blends of the following materials: HYTREL® and/or HYLENE® products from DuPont, Wilmington, Del. PEBAX® products from Elf Atochem, Philadelphia, Pa. SURLYN® products from DuPont, and/or ESCOR® or IOTEK® products from Exxon Chemical, Houston, Tex.

[0030] The Shore D hardness of the cover 14 should be about 58 or less. It is preferred that the boundary layer 14 have a hardness of between about 52-58 Shore D, more preferably from 54 to 56, and most preferably 55. One reason for preferring a cover 14 with a Shore D hardness of 52 to 58 is to improve the feel of the resultant golf ball. The Shore D Hardness is determined according to ASTM D2240. However, the comparative testing in Table Two tested the Shore D hardness on the land surface of an actual golf ball by using a Instron Shore D durometer tester while the golf ball was fixed within a holder.

[0031] It is also preferred that the cover 14 is composed of a blend of SURLYN® ionomer resins. SURLYN® 8150 and 6320 are, respectively, an ionomer resin composed of a sodium neutralized ethylene/methacrylic acid, and an ionomer resin composed of a terpolymer of ethylene, methacrylic acid and n-butyl acrylate partially neutralized with magnesium, all of which are available from DuPont, Polymer Products, Wilmington, Del.

[0032] Preferably the blend of ionomers that form the cover 14 is composed of 20 to 40 weight percent of a sodium neutralized ethylene/methacrylic acid ionomer resin ( SURLYN 8150), and 60 to 80 weight percent of an ionomer resin composed of a terpolymer of ethylene, methacrylic acid and n-butyl acrylate partially neutralized with magnesium (SURLYN 6350). A preferred embodiment is a blend of ionomers composed of 35 weight percent of a sodium neutralized ethylene/methacrylic acid ionomer resin ( SURLYN 8150), and 65 weight percent of an ionomer resin composed of a terpolymer of ethylene, methacrylic acid and n-butyl acrylate partially neutralized with magnesium (SURLYN 6350).

[0033] Preferably, the ionomer resins are mixed and heated, then injection molded in a flowable form over the core 12 in a conventional manner that is well-known to those skilled in the pertinent art to form the cover 14. The mold has an inverse aerodynamic pattern to form the aerodynamic pattern on the cover 14. Alternatively, the cover 14 may be manufactured using half shells that are compression molded over the core 12, which is also well-known in the pertinent art.

[0034] An alternative embodiment of the cover 14 may include a predetermined amount of a baryte mixture. The baryte mixture is included as 8 or 9 parts per hundred parts of the ionomer resins. One preferred baryte mixture is composed of 80% barytes and 20% of an ionomer, and is available from Americhem, Inc., Cuyahoga Falls, Ohio, under the trade designation 38534X1.

[0035] The cover 14 preferably has a thickness of 0.60 inch to 0.90 inch, most preferably ranging from 0.65 inch to 0.80 inch, and most preferably 0.70 inch.

[0036] The golf ball 10 is finished by applying a base coat and/or top coat to the surface of the cover 14 for whiteness and protection. Also, a logo marking may be applied to the base coat or top coat. The finished golf ball 10 has a weight of 45 to 46 grams, preferably 45.65 grams. The golf ball 10 has a PGA compression of 70 to 95 points, preferably 80 to 90 points, and most preferably 84 points. The golf ball 10 has a COR of 75 to 85 points, preferably 78.0 to 79.5 points, and most preferably 79.0 points at 143 fps. The golf ball 10 preferably has a diameter of approximately 1.68 inches. However, those skilled in the pertinent art will recognize that the golf ball may have a diameter that is more of less than 1.68 inches without departing from the scope and spirit of the present invention.

[0037] Table Two is a comparison of the golf ball 10 of the present invention and other competitive golf balls on the market. TABLE TWO Medium Speed Core Ball Ball Cover Ball True Spin Driver Ball Ball Compression COR Rebound Hardness Compression Sand Wedge velocity Golf ball 10 70.75 0.7896 74.8 55  84 5229 132.43 Precept MC 80.66 0.7803 74.3 50  88 6190 132.11 Spin Precept EV Extra 85.54 0.7739 74.65 55.25 103 4535 131.95 Spin Titleist HP Tour 71.70 0.7653 77.4 60  86 4391 131.16 Wilson Staff 50.37 0.7658 73.36 61  87 4011 130.94 Smart-Core Spin Distance Nike Spin 66.04 0.7765 74.86 53  83 5330 131.58 Control Maxfli XS Tour 82.03 0.7790 73.76 55  95 5430 132.02 Top Flite 71.17 0.7616 74.8 60  93 4239 130.72 XL2000 Exceptional Spin

[0038] The ball compression for each golf ball in Table Two was measured using the PGA compression test described above for several golf balls and taking the mean value. The core compression for each golf ball in Table Two was measured by removing the cover and subjecting the core of each golf ball to a PGA compression test as described above for several golf balls and taking the mean value. The Ball COR for each golf ball in Table Two was measured by firing each golf ball at 143 fps at a solid wall as described above for several golf balls and taking the mean value. The cover hardness for each golf ball in Table Two was measured on the land surface of the golf ball using a Shore D durometer as described above for several golf balls and taking the mean value. The ball rebound for each golf ball in Table Two was measured by dropping each golf ball at a predetermined height at a solid floor as measuring the rebound for several golf balls and taking the mean value. The sand wedge true spin for each golf ball in Table Two was determined by hitting each golf ball with a Callaway Golf® STEELHEAD™ X-14® sand wedge at a speed of approximately 50 miles per hour (“MPH”) for several golf balls and taking the mean value of the spin in rotations per minute. The medium speed driver ball velocity for each golf ball in Table Two was determined by hitting each golf ball with a Callaway Golf® BIG BERTHA® HAWK EYE® VFT™ ten degree driver at a speed of approximately 90 miles per hour (“MPH”) for several golf balls and taking the mean value.

[0039] As shown in FIG. 3, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 78.2 (or 0.782 unscaled) and a Shore D less 56. More specifically, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 78.8 and a Shore D less 56. Most specifically, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 79.0 and a Shore D less 56.

[0040] As shown in FIG. 4, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 78.2 and a ball compression less than 88 points. More specifically, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 78.8 and a ball compression less than 88 points. Most specifically, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 79.0 and a ball compression less than 88 points.

[0041] As shown in FIG. 5, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 78.2 and a core size between 1.53 inches and 1.55 inches. More specifically, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 78.8 and a core size between 1.53 inches and 1.55 inches. Most specifically, the golf ball 10 of the present invention is the only golf ball that has a COR greater than 79.0 and a core size between 1.53 inches and 1.55 inches.

[0042] From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claims. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims. 

We claim as our invention:
 1. A golf ball comprising: a core having a diameter of 1.50 inches to 1.56 inches, the core comprising polybutadiene, zinc oxide in an amount of 7 to 15 parts per hundred parts of polybutadiene, zinc diacryalate in an amount of 20 to 50 parts per hundred parts of polybutadiene; an initiator in an amount of 0.1 to 1.0 parts per hundred parts of polybutadiene, and tungsten in an amount of 5 to 10 parts per hundred parts of polybutadiene, the core having a PGA compression of 55 to 70 points; and a cover having a thickness of 0.60 inch to 0.90 inch, the cover comprising an ionomer blend formed from a high acid ionomer resin neutralized with zinc in a range of 20 to 40 weight percent of the ionomer blend, and a terpolymer neutralized with magnesium in a range of 80 to 60 weight percent of the ionomer blend, and a Shore D hardness ranging from 52 to 58; wherein the golf ball has a PGA compression ranging from 80 to 95 points and a COR at 143 feet per second of 78.2 to 80.5.
 2. A golf ball comprising: a core having a diameter of 1.50 inches to 1.56 inches, the core having a PGA compression of 55 to 70 points; and a cover having a thickness of 0.60 inch to 0.90 inch, the cover having a Shore D hardness less than 58 as measured on the land surface of the golf ball; wherein the golf ball has COR at 143 feet per second of 78.2 to 80.5.
 3. A golf ball comprising: a core having a diameter of 1.53 inches to 1.55 inches, the core having a PGA compression of 60 to 75 points; and a cover composed of an ionomer blend formed from a high acid ionomer resin neutralized with zinc in a range of 20 to 40 weight percent of the ionomer blend, and a terpolymer neutralized with magnesium in a range of 80 to 60 weight percent of the ionomer blend, the cover having a thickness of 0.60 inch to 0.90 inch, the cover having a Shore D hardness less than 58 as measured on the land surface of the golf ball; wherein the golf ball has COR at 143 feet per second of 78.2 to 80.5.
 4. A golf ball comprising: a core having a diameter of 1.53 inches to 1.55 inches, the core having a PGA compression of 60 to 75 points; and a cover composed of an ionomer blend formed from a high acid ionomer resin neutralized with zinc in a range of 20 to 40 weight percent of the ionomer blend, and a terpolymer neutralized with magnesium in a range of 80 to 60 weight percent of the ionomer blend, the cover having a thickness of 0.60 inch to 0.90 inch, the cover having a Shore D hardness less than 58 as measured on the land surface of the golf ball; wherein the golf ball has a COR that is greater than 0.790 points at 143 feet per second, and a true spin greater than 5200 rotations per minute off a sand wedge at a swing speed of 50 miles per hour. 